AN INTERNAL COMBUSTION ENGINE FOR AN AUTOMATED MANUAL TRANSMISSION VEHICLE

FIELD OF THE INVENTION

[0001] The present subject matter relates generally to an internal combustion engine, and more particularly but not exclusively to an internal combustion engine for a vehicle having automated manual transmission (AMT).

BACKGROUND OF THE INVENTION

[0002] A conventional two wheeled vehicle is powered by an internal combustion engine generally disposed at a 16'weFfiairof the vehicle. This engine converts chemical energy into mechanical energy by combustion of air-fuel mixture within a combustion chamber of the engine. The said engine, among other components, has a cylinder comprising a cylinder head atop or in front of the cylinder and receiving a reciprocating piston from the bottom or the rear. On combustion of the air-fuel mixture, the piston transfers the energy generated during combustion to a crankshaft through a connecting rod thereby driving the crankshaft. In this way, the reciprocatory motion of the piston is converted to rotatory motion of the crankshaft. The crankshaft is housed inside a crankcase beneath or behind the cylinder block.In order to set the vehicle into motion, the power supplied to the crankshaft of the internal combustion engine is carried to a wheel of the vehicle, in a controllable way, through a transmission system. The transmission system in the conventional vehicle employs a clutch and a gearbox with plurality of gears, wherein gear shift is achieved manually which enables gears to be selected only in an ascending or descending sequence.A gear less transmission system, called a continuously variable transmission system, is also known where the gear shift is achieved by centrifugal forces.

[0003] Generally, in two-wheeled vehicles having manual fixed gear transmission, the operation of transmission "system requires continuous attention by the operator based on the speed of the vehicle and the speed (rpm) of the engine. As the rider controls the gear shifting manually, any jerk that arises due to shifting from one gear ratio to the other doesn't cause discomfort to the rider. This is because the rider typically closes the throttle valve partially or fully before gear shifting and controls the cluch release speed thereby reducing the engine speed so that jerkiness is avoided. The rider, thus, preempts the impact of shifting from one gear ratio to the other and hence stays prepared. However, in case of a two wheeled vehicle having automated manual transmission (AMT), it is not possible for the rider to be prepared for the timing and impact of shifting from one gear ratio to the other as in such AMT type vehicles, gear shifting is electronically controlled and occurs automatically without the prior knowledge of the rider. Thus, in such AMT type vehicles, an automatic shift from one gear ratio to the other often produces discomfort to the rider, for example, in the form of a jerk. The jerkiness poses problems in the smooth rideability of the vehicle.

[0004] One of the many reasons for the occurrence of jerk during the shifting of gear ratio is sharp change in engine speed (rpm) when the gear is shifted from one gear ratio to the other electronically and subsequently followed by a substantially linear rise or fall, more in the form of a saw tooth like waveform.For instance, shifting from a first gear ratio to a second gear ratio causes a sharp decrease in engine speed from a higher rpmto a lower rpm as shown in FIG.ll. Subsequently, the engine speed rises againin a linear fashion before dropping again during the consecutive shift in gear ratio. Accordingly, a similar trend continues depending on the number of gear ratios. Thus, the drop in engine speed is significantly high and the drop progressively decreases during shift from the first gear to higher gears. The engine speed drop is hence not uniform. Likewise, shifting from the third gear ratio to second gear ratio and, from second gear ratio to the first gear ratio causes a sharp increase in engine speed each time from a lower rpm to a higher rpm. Thus, for every consecutive shift in gear ratio, the sharp fall or rise in engine speed tends to gradually reduce or increase, thereby causing a substantial jerk during the shifting in gear ratios. Such occurrence of jerk causes discomfort to the rider who is unaware of the timing and impact of the shift in gear ratio in the AMT vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The above and other features, aspects, and advantages of the present invention will be better understood with regard to the following description where:

FIG. 1 is an assembly view of an engine for an AMT vehicle..

FIG.2 is a sectional view for a gear shift actuator system installed in the engine of FIG; 1.

FIG.3 shows a side view of the gear shift actuation system without a clutch cover.

FIG. 4 shows assembly of the engine of FIG. 1.

FIG. 5 shows a sectional view of the mating gears in a transmission system within the engine of FIG. 1.

FIG. 6 shows a table of ratio of pre-determined gear ratio between two consecutive pairs of mated gears and its values according to an embodiment of the present invention.

FIG. 7 shows, a table of ratio of pre-determined gear ratio between two consecutive pairs of mated gears and its values according to a second embodiment of the present invention.

FIG. 8 shows the relationship between the engine speed and vehicle speed during— shifting of gear ratios in a five speed transmission system according to the embodiment of FIG. 6.

FIG. 9 shows the relationship between the engine speed and vehicle speed during shifting of gear ratios in a six speed transmission system according to the embodiment of FIG. 6.

FIG. 10 shows the relationship between the engine speed and vehicle speed during shifting of gear ratios in a five speed transmission "system according to the second embodiment of FIG. 7.

FIG. 11 shows the relationship between the engine speed and vehicle speed during shifting of gear ratios according to the prior art.

BRIEF DESCRIPTION OF THE INVENTION

[0006] The present invention removes one or more problems as mentioned above and obviate a lacunae in the prior art. One of the object of the present invention is to provide an internal combustion (IC) engine for an AMT vehicle with reduced jerkiness during gear shifting and improved rideability. The invention is now explained.

[0007] FIG. lshows a side view of an engine lOOfor an AMT vehicle
having a cylinder head 101 and a transmission system disposed internal to a clutch cover 102. The transmission system has an automatic clutch 212shown in FIG. 4 connected to the engine to disengage the engine from the transmission system during the shifting of gear ratios. The operation of clutch 212 is electronically controlled through a clutch actuation system provided therein. The clutch actuation system for actuating the operation of clutch engagement and disengagement includes a clutch actuation motor 105, a reduction gear box comprising of a plurality of reduction gears attached to the clutch actuation motor 105 and a power transmission mechanism which transmits the rotational driving force of the clutch actuation motor 105. A clutch position sensor is also provided to detect the actual position of the clutch. The clutch actuation motor 105 is mounted and secured to an outer surface of the clutch cover 102 and sealed against ingress of oil. The clutch actuation motor 105 is electrically connected to a controller (not shown) which may be programmed to control the direction of rotation of the clutch actuation motor 105 as well as the time duration of its operation.

[0008] The automatic clutch 212 is electrically operated through the clutch actuation motor 105 via the power transmission mechanism for clutch. In an embodiment, the power tranmission system for clutch comprises of a worm gear 108 operatively meshed with a worm wheel HO.Additionally, for emergencies, a manually operated clutch release lever 121 is provided which is operatively connected with a clutch release shaft 125. The clutch release shaft 125 is operatively connected with a clutch release pin (not shown). After the clutch is disengaged, the gear shift is undertaken electronically through a gear shift actuator system.

[0009] The gear shift actuator system is positioned laterally to the engine towards the clutch side as shown in FIG. 3. The engine contains the cylinder head 101 and a cylinder block 22 incorporating a piston (not shown). It is started by a starter lever placed on the starter shaft 209 or by a starter motor 23. A gear shift motor 201 is mounted to an external surface of the clutch cover 102 and sealed against ingress of oil. A reduction gear box 202 is connected to the gear shift motor 201 for reducing the power received from the said gear shift motor 201. A power transmission mechanism transmits rotational driving force of the said gear shift motor 201 to a shift drum 210 wherein the shift drum 210, turnably supported by a crankcase 24, is driven by the said gear shift motor 201 to select the desired gear ratio. The gear shift motor 201 is capable of rotating in both, normal and reverse directions and is electrically connected to the controller which is programmed to control the direction of rotation of the gear shift motor 201 as well as the time duration of its operation.

[00010] In an embodiment, the power transmission system for gear shifting comprises of a rack and pinion approach through which the gear shift motor 201transmits power to the shift drum 210. However, other ways of power transmission for gear shifting are also possible. The gear shift motor 201has an. output shaft over which a drive gear 203 is mounted. A cone clutch arrangement may be adapted to protect the mechanism from end stops and dog outs. The drive gear 203 is mated with a pinion 205 supported interior to the clutch cover 102. The pinion 205 engages with a driving rack 204 that is slidably supported on the crankcase interior through a pawl 206 present at an anterior portion of the rack 204. The pawl and the rack have a joint between them. The pawl 206 contains partial projections which rotate the shift drum 210 through a star index 207. A stopper 208 is provided to keep the shift drum 210 in the selected gear ratio so that it does not shift automatically. The rack and pinion assembly incorporates a centering spring 214 to ensure return to neutral position. The rack and pinion arrangement during assembly is hidden by the automatic clutch 212 mounted on a countershaft 213 and anterior to the star index 207.

[00011] The working of the gear shift actuator system is now explained. The controller is programmed to drive the gear shift motor 201 according to the riding conditions (e.g. engine speed or throttle position). The gear shift actuation takes place only after the clutch has been disengaged; The reduction gear box 202 reduces the output of the gear shift motor 201 so as to optimally rotate the drive gear 203. The drive gear in turn rotates the pinion 205 which then slides the rack 204. The resultant force pushes the pawl 206 which turns the star index 207 by a certain degree, the rotation being enough to change the gear ratio. According to an embodiment of present invention, the star index is to be turned between 60-72 degrees for effectuating a gear shift resulting into a gear change. The star index is then kept in this position by the stopper 208.A shift position detector detects the current gear ratio and provides input to the shift control unit. The rotation of the gear shift motor 201 can be reversed for a reverse operation. Thus the shift drum 210 will rotate in. the same direction as that of the gear shift motor 201. As the shift drum rotates, the gear shift has been actuated and the shift fork (not shown) locks free running gears to their shaft thereby effecting a gear shift.

[00012] The gear shift motor 201 and the reduction gear box 202 are supported and secured on an external surface of the clutch cover 102 in a housing 211 in a lateral direction i.e. parallel to crankshaft axis and lateral to the rack axis. The drive gear 203 is interior to the clutch cover 102.

[00013] During the electronically controlled gear shift, the jerkiness feeling is overcome when the change inengine speed is contained or is not very sharp so that it becomes less noticeable to the vehicle rider. To this end, the present invention provides an AMT system for a two wheeled vehicle or a three wheeled vehicle that optimally shifts gear ratio without producing substantial jerk that . causes discomfort to the. rider. The AMT system has a plurality of gears defining a pre-determined gear ratio between a pair of mated gears. For achieving a negligible jerk feel during the shifting, a ratio of said pre-determined gear ratio between two consecutive pairs of mated gears is at least 1.14 when a shifting occurs from a first pre-determined gear ratio to a second pre-determined gear ratio. In an embodiment, the ratio of said pre-determined gear ratio between two consecutive pair of mated gears is at least between 1.14 and 1.40.

[00014] FIG. 6 shows a table of ratio of pre-determined gear ratio between two consecutive pair of mated gears and its values. In the embodiment where the shifting takes place from the first gear ratio to the second.gear ratio, the ratio between the first gear ratio to the second gear ratio is 1.14. In an implementation, when the shifting takes place from the second gear ratio to the third gear ratio, the ratio between the second gear ratio to the third gear ratio is 1.31. In an implementation, when the shifting takes place from the third gear ratio to the fourth gear ratio, the ratio between the third gear ratio to the. fourth gear ratio is 1.28. In an implementation, when the shifting takes place from the fourth gear ratio to the fifth gear ratio, the ratio between the fourth gear ratio to the fifth gear . ratio is 1.30.To achieve the optimal gear shifting with less noticeable jerk, the AMT system of the present invention includes at least five pairs of mated gears with five different gear ratios within the transmission casing.As shown in FIG. 5, in an implementation, the five pairs of mated gears comprises a first drive gear 301 having at least 13 teeth, a second drivegear 302 having at least 14 teeth, a third drivegear 303 having at least 16 teeth, a fourth drivegear 304 having at least 19 teeth and a fifth drivegear 305 having at least 20 teeth. In an embodiment, the five pair of mated gears is disposed in a four speed transmission casing which saves space despite adding more gears.

[00015] In proportion to the vehicle speed, the engine speed is very high in the initial gear ratios to provide sufficient torque for enabling adequate pulling capacity to vehicle. Therefore, any sudden and significant change in the engine speed during the shifting of initial gear ratios is felt by the rider. When the ratio of pre-determined gear ratio between two consecutive pairs of mated gears is at least 1.14,. the change in engine speed is not sharp as shown in FIG. 8 and the consecutive change in the engine speed when shifting from one gear ratio to another gear ratio is approximately on the same base line. For instance, when the gear is upshifted from first gear ratio to second gear ratio, the engine speed decreases during the gear shift with the aforementioned gear ratio configuration. The engine speed then linearly rises again. Subsequently, when the gear is shifted from second gear ratio to third gear ratio and so on, the engine speed again decreases from the previous peak but it does not fall significantly below the previous engine speed trough. The decrease in engine speed is thus approximately uniform along the same baseline. Thus, for every consecutive shift in the gear ratio, the decrease in the engine speed tends to remain uniform. The magnitude of the change in engine speed also reduces. Thus, the change in engine speed during shifting across gear ratios is uniform as well as low in the AMT vehicle even though the gear shift is electronically controlled.Consequently, no noticeable jerk is felt by the vehicle rider of the AMT vehicle.

[00016] A similar arrangement is possible with a six speed automatic transmission system in whichwhen the shifting takes place from the first gear ratio to the second gear ratio, the ratio between the first gear ratio to the second gear ratio is at least 1.14. When the shifting takes place from the second gear ratio to the third gear ratio, the ratio between the second gear ratio to the third gear ratio is 1.18. When the shifting takes place from the third gear ratio to the fourth gear ratio, the ratio between the third gear ratio to the fourth gear ratio is 1:20. When the shifting takes place from the fourth gear ratio to the fifth gear ratio, the ratio between the fourth gear ratio to the fifth gear ratio is 1.22. When the shifting takes place from the fifth gear ratio to the sixth gear ratio, the ratio between the fifth gear ratio to the sixth gear ratio is 1.26. The six speed automatic transmission system includes at least six or more pairs of mated gears wherein the six pair of mated gears comprises a first drive gear having at least 13 teeth, a second drive gear having at least 14 teeth, a third drive gear having at least 16 teeth, a fourth drive gear having at least 18 teeth and a fifth drive gear having at least 22 teeth. For the six speed transmisison, the change inengine speed is not sharp in gear shift as shown in FIG. 9. Because the engine speed is not high at later gear ratios and the gear shfiting is spaced out, the change in engine speed is not felt.

[00017] In a second embodiment, the ratio of said pre-determined gear ratio between two1 consecutive pairs of mated gears is between 1.25 and 1.35. As shown in FIG. 7, in the second embodiment where the shifting takes place from the first gear ratio to the second gear ratio, the ratio between the first gear ratio to the - second gear ratio is 1.35. Therefore when the gear shifting takes place from first gear ratio to second gear ratio, the drop in engine speed is not sharp. In an implementation, when the shifting takes place from the second gear ratio to the third gear ratio, the ratio between the second gear ratio to the third gear ratio is 1.27. In an implementation, when the shifting takes place from the third gear ratio to the fourth gear ratio, the ratio between the third gear ratio- to the fourth gear ratio is 1.26. In an implementation, when the shifting takes place from the fourth gear ratio to the fifth gear ratio, the ratio between the fourth gear ratio to the fifth gear ratio is 1.27. For this implementation, the five pair of mated gears comprises a first drive gear having at least 12 teeth, a second drive gear having at least 13 teeth, a third drive gear having at least 16 teeth, a fourth drive gear having at least 18 teeth and a fifth drive gear having at least 20 teeth.When the ratio of pre¬determined gear ratio between two consecutive pair of mated gears is between 1.25 and 1.35, the change in engine speed is not sharp as shown in FIG. 10 and the consecutive change in the engine speed when shifting from one gear ratio to another gear ratio is approximately on the same base line.Thus, the change is engine speed during shifting across gear ratios is uniform as well as low in the AMT vehicle even though the gear shift is electronically controlled. The present invention thus reduces the noticeable change in the engine speed "during every gear shift and consequently, no noticeable jerk is felt by the vehicle rider of the AMT vehicle.

[00018] The present subject matter is thus described. The description is not intended to be exhaustive, nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above description. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various- embodiments and with various modifications as are suited to the particular use contemplated. Therefore the forgoing description is to be considered exemplary, rather than limiting, and the true scope of the -invention is that described in the appended claims.

I/We claim:

1. An internal combustion engine (IC) (100) comprising an automatic transmission system having a plurality of gears defining a pre-determined gear ratio between a pair of mated gears, wherein a ratio of said pre-determined gear ratio between two consecutive pairs of mated gears is at least 1.14when a shifting occurs from a first pre-determined gear ratio to a second pre-determined gear ratio. -

2. The IC engine (100) as claimed in claim 1, wherein the ratio of said ^ „...-„ pre-determined gear ratio between two consecutive pairs of mated gears is at least between 1.14 and 1.40.

3. The IC engine (100) as claimed in claim 1, wherein the automatic transmission system includes at least five pair of mated gears.

4. The IC engine (100) as claimed in claim 3, wherein the five pair of. mated gears is disposed in a four speed transmission casing.

5. The IC engine (100) as claimed in claim 3, wherein the five pair of mated gearsinclude a first gear having at least 13 teeth, a second gear having at least 14 teeth, a third gear having at least 16 teeth, a fourth gear having at least 19 teeth and a fifth gear having at least 20 teeth.

6. The IC engine (100) as claimed in claim 3, wherein the ratio of said pre-determined gear ratio between the second pair of mated gears and the third pair of mated gears is at least 1,21.

7. The IC engine (100) as claimed in claim 1, wherein the automatic transmission system includes at least six pair of mated gears.